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Author Topic: Image wrecked by SRGB conversion  (Read 8095 times)
Graystar
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« Reply #20 on: December 09, 2011, 07:27:42 AM »
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I'm viewing this image in Firefox (color managed) and I see a drastic difference between the ProPhoto image and the SRGB image. Both files show the same differences when viewed in Photoshop as well.

If that's the case then I'd suggest the possibility that your color management is misconfigured.  The images should look exactly the same in a color managed application because the ProPhoto version should have been converted into the monitor's color space for display.  And I'm pretty sure that there are no monitors that cover the ProPhoto space.  sRGB and Adobe RGB red points are the same, so this particular pair of images should look the same even on a properly configured wide-gamut monitor.

Without color management you get the same problem as viewing an AdobeRGB image in any color-dumb application...desaturation, but no clipping as the numeric ProPhoto values are being interpreted as sRGB or monitor-profile values.  Which is exactly what I see when I turn off color management in my viewer.

In Raw Therapee the ProPhoto version is easily recoverable, while the sRGB version is a total loss, so I'm pretty sure I've got the right files.  But in IE 9 and every other color managed application I have, they look the same.

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FranciscoDisilvestro
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« Reply #21 on: December 09, 2011, 07:55:29 AM »
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If that's the case then I'd suggest the possibility that your color management is misconfigured.  The images should look exactly the same in a color managed application because the ProPhoto version should have been converted into the monitor's color space for display.  And I'm pretty sure that there are no monitors that cover the ProPhoto space.  sRGB and Adobe RGB red points are the same, so this particular pair of images should look the same even on a properly configured wide-gamut monitor.


The sRGB and AdobeRGB red primaries are the same only at L=50. If you compare the 3D gamut plots of both spaces youŽll see that there are differences at other values of L.

Besides that, the jacket is not pure red, it has some yellow (R and G), and there is where the differences between sRGB and AdobeRGB are.

The attached image shows the difference in gamut warning when softproofing to AdobeRGB (left) and sRGB(rigth) after a saturation adjustment of the original ProphotoRGB version. If you use a wide gamut monitor, there should be differences (maybe not "drastic").
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Graystar
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« Reply #22 on: December 09, 2011, 08:27:41 AM »
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The attached image shows the difference in gamut warning when softproofing to AdobeRGB (left) and sRGB(rigth) after a saturation adjustment of the original ProphotoRGB version.

What's the gamut warning before the saturation adjustment?
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FranciscoDisilvestro
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« Reply #23 on: December 09, 2011, 10:17:32 AM »
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What's the gamut warning before the saturation adjustment?

There is a small (not null) difference in the gamut warning before the saturation adjustment, due to the fact that the red channel is not the only one involved. Sometimes we think about blown channels when they reach saturation (255) but not when they reach zero (0).

What happens is that the mathematical conversion of a specific color from one color space to the other could result in a negative theoretical value in one of the channels (this can be easily tested using Bruce Lindbloom CIE Color Calculator). In this case the value is set to zero (0) and it doesn't look as a blown out value, but it is a different color than it should be. How far is this color? It is not possible to determine with the gamut warning.

As an example, a sample value from the chest area has R=174; G=44; B=22 in ProPhotoRGB. The theoretical value for AdobeRGB would be R=215; G=-71; B=8 and for sRGB R=254; G=-69; B=10. The resulting images in PS will show the Adobe RGB image with G=0 and the red channel below saturation and the sRGB image with G=0 and the Red channel clipped. Both are really out of gamut, but the fact that the Red channel is not clipped in the AdobeRGB version make it look as it is inside the gamut of AdobeRGB.

To show this, the attached files show the red and green channels using the threshold function of PS to show red areas a 255 and green areas at 0. The original ProPHotoRGB version don't have either red values at 255 nor green values at 0. This images show how large is the effect of the green channel.

The AdobeRGB version is at the left, the sRGB to the right. First image shows Red channel threshold at 255, the other the green channel threshold at 0.

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Sheldon N
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« Reply #24 on: December 09, 2011, 10:32:58 AM »
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If that's the case then I'd suggest the possibility that your color management is misconfigured.  The images should look exactly the same in a color managed application because the ProPhoto version should have been converted into the monitor's color space for display.  And I'm pretty sure that there are no monitors that cover the ProPhoto space.  sRGB and Adobe RGB red points are the same, so this particular pair of images should look the same even on a properly configured wide-gamut monitor.

Without color management you get the same problem as viewing an AdobeRGB image in any color-dumb application...desaturation, but no clipping as the numeric ProPhoto values are being interpreted as sRGB or monitor-profile values.  Which is exactly what I see when I turn off color management in my viewer.

In Raw Therapee the ProPhoto version is easily recoverable, while the sRGB version is a total loss, so I'm pretty sure I've got the right files.  But in IE 9 and every other color managed application I have, they look the same.

Maybe you are misunderstanding what I am saying.

The ProphotoRGB crop of image in the original post looks the same to me whether I view it in Firefox or Photoshop. Very saturated, but good definition of colors/tones/lights/shadows.

The sRGB conversion crop of the image in the original post looks the same to me whether I view it in Firefox or Photoshop. Loss of saturation, tones compressed, loss of detail/highlight/shadow definition. As you said, a total loss.

The reds in Adobe RGB are definitely not the same as the reds in sRGB, especially in the brighter tones. A straight conversion of the ProPhoto RGB image to Adobe RGB does much less damage than converting it to sRGB. Try it in Photoshop and see.

My monitor is the 2408WFP which has a gamut larger than Adobe RGB, especially in the reds. I can easily see the saturation difference between ProPhotoRGB and Adobe RGB, both in how they render the image and in top end saturation.
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Pete Berry
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« Reply #25 on: December 09, 2011, 01:40:23 PM »
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.......My monitor is the 2408WFP which has a gamut larger than Adobe RGB, especially in the reds. I can easily see the saturation difference between ProPhotoRGB and Adobe RGB, both in how they render the image and in top end saturation.

Graystar's experience seems to be the same confusing one as mine with the PP- and sRGB images essentially identical in CS5. My 4 year old Gateway LP2407 monitor simply lacks the gamut to display the saturated PP reds that wider gamut monitors obviously can.

Although I've had a few instances where my PP-16 bit images showed small patches of in-gamut reds that displayed poorly while printing nicely, this is a first for such a graphic example. The Dell 2408 WFP looks like a nice, affordable wider gamut choice to keep in mind.
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Graystar
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« Reply #26 on: December 09, 2011, 02:02:43 PM »
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The AdobeRGB version is at the left, the sRGB to the right. First image shows Red channel threshold at 255, the other the green channel threshold at 0.

My monitor is the 2408WFP which has a gamut larger than Adobe RGB, especially in the reds. I can easily see the saturation difference between ProPhotoRGB and Adobe RGB

Okay...that explains some things.
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